The present invention relates to a semiconductor, an n-type semiconductor, a p-type semiconductor, a semiconductor junction device, a pn junction device and a photoelectric converter. The present invention relates, in particular, to a semiconductor junction device employing a p-type semiconductor and a photoelectric converter employing a p-type semiconductor.
Iron sulfide, which has a high optical absorption coefficient, is therefore expected to be applied to a light receiving and emitting device. If application is considered here, at least a conductive type control (pn control) technique is indispensable, and energetic researches and developments therefor are conducted. It is known that the reception and emission wavelengths of light are largely influenced by the forbidden bandwidth of the semiconductor. With regard to iron sulfide, the forbidden bandwidth is about 0.95 eV even in the case of FeS2 single crystal that has the greatest forbidden bandwidth. In order to widen the application range, it is earnestly demanded to develop the forbidden bandwidth control (particularly forbidden bandwidth widening) technique.
As iron sulfide, the compositions of FeS, FeS2 and Fe2S3 are known. The iron valence of FeS and FeS2 is bivalent, whereas the iron valence of Fe2S3 is trivalent. In this case, Fe2S3, which is unstable and is decomposed into FeS and FeS2 and easily decomposed into an iron oxide hydrate and sulfur in a wet air, is not suitable for application.
It is known that iron sulfide exhibits the p-type conductivity if sulfur is excessive or exhibits the n-type conductivity when sulfur is insufficient as compared with the stoichiometry when impurity doping is not performed.
On the other hand, energetic researches are conducted on the control of the conductive type by doping iron sulfide with an impurity.
For example, JP S61-106499 A discloses that, if a photoactive pyrite layer in which the stoichiometric deviation of a pyrite material conforms to a formula: FeS2±X [0<x≦0.05], the impurity concentration has a value smaller than 1020 per 1 cm3, a doping material of manganese (Mn), arsenic (As), cobalt (Co) or chlorine (Cl) is used, and the doping concentration of the doping material is about 1016 to 1019 per 1 cm3 is applied to a solar cell, then the solar cell exhibits a satisfactory characteristic. There is a further disclosure that the n-type conductivity is obtained by doping pyrite FeS2 with Ni or Co, and the p-type conductivity is obtained by doping pyrite FeS2 with Cu or As.
Moreover, JP 2002-516651 A discloses that a semiconductor component in which a semiconductor substrate made of pyrite having at least partially a chemical composition FeS2 is combined with at least one of boron (B) and phosphorus (P) or semiconductor components doped with the substances are most suitable and extremely efficient for use in applications for solar cells.
However, the techniques disclosed in JP S61-106499 A and JP 2002-516651 A have a problem that the conductive type control (pn control) is insufficient. For example, taking JP 2002-516651 A as an example, the technique described there mentions nothing about the matters necessary for practical use regarding which conductive type the dopants of boron (B) and phosphorus (P) become and so on, and this is still problematically a long way from practical use. Moreover, taking a full solid type solar cell that uses pyrite FeS2 in the photoactive layer as an example, there is a problem that the photoelectric conversion efficiency comes to have a very low value of not greater than 1% in the full solid type solar cell as in the Schottky type diode structure and the like attributed to the fact that the conductive type control (pn control) is insufficient, as described in P. P. Altermatt, et al.; Solar Energy Materials & Solar Cells 71 (2002) p. 181 (Hereinafter, referred to “Altermatt, et al.”).
Furthermore, JP S61-106499 A and JP 2002-516651 A mention nothing about a technique for controlling the forbidden bandwidth but the doping technique for conductive type control. Moreover, Altermatt, et al. and its cited documents have descriptions of the possibility of an increase in the forbidden bandwidth if FeS2 is doped with zinc, but they do not show the ground therefor experimentally and theoretically, and no concrete practicable description exists in the above described document and its cited documents. Thus, it is the present condition that no established method is available as to the method for controlling the forbidden bandwidth of iron sulfide, and the method for controlling the forbidden bandwidth of iron sulfide is not known. Accordingly, it is demanded to clarify the method for controlling the forbidden bandwidth of iron sulfide.